Numerous advances of considerable note have occurred in medical surgical techniques over the last few decades. Among the most significant advances has been the adoption, and now-routine performance, of a wide variety of minimally invasive procedures. When carrying out such procedures, access to a site of concern within a patient is achieved through a relatively small incision, into which a tubular device (such as a sheath) is inserted or introduced. The sheath keeps the incision open while permitting access to the target site via the interior (i.e., lumen) of the sheath. Non-limiting examples of such devices include introducer sheaths, guide catheters, and like devices (devices collectively referred to herein as “sheaths” or “introducer sheaths”).
Body passageways in which medical interventional devices, such as stents, are now commonly introduced include the esophagus, trachea, colon, biliary tract, urinary tract, and vascular system, among other locations within the body. When placing a medical interventional device in a passageway, communication with the passageway is typically attained by initially inserting the distal end of the introducer sheath into the body passageway. Since the introducer sheath must often traverse tortuous passageways to reach the target site, the sheath often includes a coil reinforcement to enhance the flexibility of the sheath, and thereby, facilitate passage of the sheath through the passageway without kinking. Examples of introducer sheaths of this type are described in U.S. Pat. No. 5,380,304, and U.S. Pat. Publ. No. 2001/0034514, both incorporated by reference herein.
The sheaths described in these patent documents include a lubricious inner liner and a helical coil fitted over the liner. The coil is typically formed from flat wire, i.e., wire having a substantially rectangular cross-section. Utilizing a flat wire coil enables the sheath to maintain the smallest possible wall diameter, while at the same time providing suitable radial support to the sheath. An outer tube is formed of a composition, such as a polyether block amide or a polyamide (nylon), that provides sufficient flexibility to the sheath so that it can bend along the tortuous passageways.
The medical interventional device, such as an expandable stent, etc., is delivered to the target site from a lumen in the introducer sheath. Typically, the device is deployed at the target site by withdrawing the introducer sheath from around the stent while the stent is in a constricted condition. An inner catheter may be provided in the sheath lumen for preventing the stent from withdrawing with the sheath. In an alternative arrangement, the constricted stent may be pushed from the distal end of the sheath by a pusher mechanism positioned in the sheath lumen. In either technique, upon deployment from the sheath at the target site, the device expands to the diameter of the surrounding body passageway.
Deployment of expandable medical interventional devices, such as stents, in this manner is now a routine practice, and such deployment is often carried out with only a minimum of complications, if any. This is particularly true when such devices have a relatively short length (e.g., less than about 80 mm) and/or a relatively modest outer diameter. However, as medical technology has progressed, stents and other interventional devices having longer lengths (e.g., about 100 to 300 mm or more) and/or having outer coatings, coverings, etc., that increase the effective outer diameter of the stent have become more common. When such stents are placed in a sheath lumen for delivery to the target site, the greater length and/or outer diameter of the stent increases the deployment forces necessary to extract the stent from the sheath when compared to shorter and/or lesser diameter stents. This increase in deployment forces is due primarily to the increased radially outwardly-directed forces exerted by the longer and/or greater diameter stents on the interior wall of the sheath.
In this event, an introducer sheath having a coiled reinforcement as described above has a tendency to stretch longitudinally as it is withdrawn from around the interventional device. Although this phenomenon may occur on some occasions with non-coated, non-covered, or shorter interventional devices, it is more pronounced with the coated, covered, or longer diameter devices that exert increased deployment forces on the interior wall of the sheath. With such coated, covered, or longer diameter devices, the stretching of the sheath causes the distance between adjacent turns of the coil to increase. This longitudinal expansion of the reinforcing coil adversely affects the ability of the sheath wall to withstand the radial expansive forces exerted on the interior of the wall by the stent, which can result in the formation of pockets along the wall of the sheath between adjacent coil turns. When this occurs, surfaces of the undeployed stent may expand into such pockets, thereby undesirably increasing the resistance imparted by the stent upon the sheath, and hindering efficient deployment of the stent. In addition, the sheath may elongate as it is withdrawn from the stent. When such elongation occurs, the distance the sheath handle travels is reduced, which may prevent the stent from being fully deployed in the vessel from the sheath.
It is desired to provide an improved introducer sheath or other medical apparatus suitable for traversing tortuous passageways in the patient's anatomy during deployment of a medical interventional device, such as an expandable stent. More particularly, it is desired to provide an improved introducer sheath that is capable of efficiently deploying interventional devices that exert high radial forces on the sheath during deployment.